The separation of mixtures into their components is one of the most important processes of the chemical industry. A common procedure for performing this separation is distillation, and numerous petroleum refining processes employ fractionator-reboiler apparatus for performing distillation of hydrocarbon mixtures.
In the most conventional distillation method, a hydrocarbon feed mixture is introduced into a fractionator column and the mixture is segregated in the column with the lower boiling constituent concentrating in a vapor phase as it migrates upwardly in the column, while the higher boiling constituent, in which any particulate material present tends to concentrate, flows downwardly in the column in a liquid state. A portion of the heavier particulate-containing liquid is withdrawn from the lower, or so called kettle, portion of the column, vaporized in a reboiler and returned to the kettle portion of the column to supply heat requirements of the distillation process.
The choice of reboiler apparatus will be dependent on the heat requirements of the distillation process. Generally, the reboiler comprises a shell and tube heat exchanger of the evaporative type which is employed for vaporization of the fractionator bottoms liquid and wherein the vaporization occurs in the shell of the reboiler.
A typical reboiler of this type comprises: a horizontally oriented shell having an inlet for process liquid and an outlet for vaporized process fluid; an inlet and an outlet for the heating medium which may be either steam or a hot process fluid; a plurality of tubes disposed in the shell so as to form a tube bundle; a tube sheet for supporting the tubes at one end, a dividing plate that cooperates with the tube sheet forming a heating fluid inlet header at one end of the tube bundle and a heating fluid outlet header at the other end of the tube bundle; transverse baffles for side-to-side flow of process liquid across the tubes; and a weir positioned within the shell to insure that liquid level in the shell is maintained and that tube surface is not exposed, with further provisions for removal of a portion of the process liquid supplied to the reboiler through a separate liquid outlet on the discharge side of the weir so that only a portion of the process liquid supplied to the reboiler is vaporized. The excess unvaporized liquid supplied to the reboiler is withdrawn from the reboiler as reboiler product. Typically, the evaporating type of reboiler also includes an empty volume of about 40% of the total shell volume located above the liquid level in the shell for disengagement of liquid-vapor mixture generated in the reboiler.
If the fractionator bottoms malaria 1 is a contaminated liquid containing solid particles or sludge, which is often the case, the area on the inner surface of the shell below the tube bundle can become virtually plugged with accumulations of these solids. Unless these accumulations are promptly removed, corrosion and fouling of the reboiler can occur.
Accordingly, it is an object of this invention to reduce the accumulation of solid particles which cause fouling of a reboiler supplying heat for a distillation process.
It is another object of this invention to maintain efficiency and capacity of a reboiler by the continuous or intermittent sparging and flushing of solid or semisolid accumulations from the shell of a shell and tube reboiler.
It is a further object of this invention to flush out accumulations of deposits while the evaporative type reboiler is in service for supplying heat to a fractionator column.